https://playground.babylonjs.com/#3VHED7#2
If you wait a little while, then move the camera with the mouse and/or the WASD keys - some or all of the lines disappear.
I think this is related to size of the scene, clipping or something else.
Help please avoid this effect ?
Thanks
Hey welcome back 
so this is because when we “morph” a line from a previous one we do not automatically update the bounding box, so at some point the lines will disappear because they will be removed by the frustum culling
Just add this line to fix your problem:
links_arr[i].geom.alwaysSelectAsActiveMesh = true;